The present invention relates to control systems, and more particularly, to a method of determining the weight of the controlled and manipulated variables of a robust multivariable predictive controller (RMPC) utilizing range control.
In current systems, the controller (RMPC) has no idea of the importance of the controlled variables and manipulated variables, thus requiring the operator (or engineer) to "tell" the controller which is the most important variable, the second most important variable, . . . or if the variables are of equal importance. The user inputs the importance (or weight) of the variables as part of the initialization procedure of a robust multivariable predictive controller. The importance of the controlled variables (cv) or manipulated variables (mv) is a function of several factors, including the units utilized for the cvs and mvs. Engineers currently account for the units for the cvs and mvs and attach an importance to the high-low weights of the cvs and mvs.
Assume for example there are three controlled variables, cv1, cv2, and cv3, where cv1 is a temperature, cv2 is a pressure, and cv3 is a concentration variable of the process, all of course in different engineering units. In this instance one controlled variable can be more important to the controller than another controlled variable. If the pressure is in small engineering units (PSI) which can have a range up to 25,000 PSI, each unit of pressure change may not be as important as 1.degree. of temperature change for the process. If the pressure, however, is in atmospheres, then one atmosphere change in pressure may be more significant then 1.degree. of temperature change.
In the present invention, there is provided an optimal solution for an RMPC in the off-line that will determine in a relative sense how important each cv and mv is to the process. Thus, the operator does not have to be concerned with making the determination. The user can still override or fine-tune the solution output (i.e., the weight for the individual variables can be made more or less), however, the present invention provides the user with an excellent starting point for initializing the controller.
Thus by attaching a weight to the variables of the process, the impact to the system is reduced and results in a more robust controller.